Mechanical couplings for joining pipe elements together end-to-end comprise interconnectable segments that are positionable circumferentially surrounding the end portions of co-axially aligned pipe elements. The term “pipe element” is used herein to describe any pipe-like item or component having a pipe like form. Pipe elements include pipe stock, pipe fittings such as elbows, caps and tees as well as fluid control components such as valves, reducers, strainers, restrictors, pressure regulators and the like.
Each mechanical coupling segment comprises a housing having projections which extend radially inwardly from the housing and engage, for example, the outer surfaces of plain end pipe elements, pipe elements having a shoulder and bead, or circumferential grooves that extend around each of the pipe elements to be joined. Engagement between the projections and the pipe elements provides mechanical restraint to the joint and ensures that the pipe elements remain coupled even under high internal pressure and external forces. The housings define an annular channel or pocket that receives a gasket or seal, typically an elastomeric ring which engages the ends of each pipe element and cooperates with the segments and the pipe elements to provide a fluid tight seal. The segments have connection members, typically in the form of lugs which project outwardly from the housings. The lugs are adapted to receive fasteners, such as nuts and bolts, which are adjustably tightenable to draw the segments toward one another.
The projections on prior art couplings typically have arcuate surfaces with a radius of curvature that is substantially matched to the radius of curvature of the outer surface of the pipe element that is to be engaged. For couplings used with grooved pipe elements, the radii of curvature of the arcuate surfaces are smaller than the radii of curvature of the outer surfaces of the pipe elements outside of the grooves so that the arcuate surfaces fit within and engage the grooves.
Methods of securing pipe elements in end to end relation comprise a sequential installation process when mechanical couplings according to the prior art are used. Typically, the coupling is received by the technician with the segments bolted together and the ring gasket captured within the segments' channels. The technician first disassembles the coupling by unbolting it, removes the ring seal, lubricates it (if not pre-lubricated) and places it around the ends of the pipe elements to be joined. Installation of the ring gasket often requires that it be lubricated and stretched to accommodate the pipe elements. With the ring gasket in place on both pipe elements, the segments are then placed one at a time straddling the ends of the pipe elements and capturing the ring gasket against them. During placement, the segments engage the gasket, the projections are aligned with the grooves, the bolts are inserted through the lugs, the nuts are threaded onto the bolts and tightened, drawing the coupling segments toward one another, compressing the gasket and engaging the projections within the grooves.
As evident from the previous description, installation of mechanical pipe couplings according to the prior art typically requires that the technician totally disassemble and reassemble the coupling while handling at least seven individual piece parts (and more when the coupling has more than two segments). Significant time, effort and expense would be saved if the technician could install a mechanical pipe coupling without first totally disassembling it and then reassembling it, piece by piece.
FIG. 1 shows a coupling 11 having coupling segments 13 and 15. The segments are joined end to end by connection members 17 and 19, the connection members including threaded fasteners 21. The segments 13 and 15 are shown supported in spaced relation from one another on the outer surface of the ring gasket 23 captured between the segments. When the segments are supported in this manner it is possible to insert pipe elements into the central space 25 between the segments without disassembling the coupling. However, there are some drawbacks to this solution to the problem of installing mechanical couplings. Note in particular that there is a limit on the pipe element diameter tolerance variations which can be accepted by coupling 11. If the pipe elements are sufficiently out of round, or if their ends are flared near the maximum degree permitted by specification, it will be difficult to impossible to insert them into the central space 25 between the segments 13 and 15, as the pipe elements will not get past the projections 29 which extend into the central space. Furthermore, the ring gasket itself can resist pipe element insertion when the distortion is not controlled. Many mass produced pipe elements are out of round to some degree and roll grooved pipe elements may be flared to some degree. Use of the coupling 11 therefore places tighter tolerances on these parameters, limiting the pipe elements which can be effectively used with such couplings and making the pipe elements more expensive as they must either be “selected” pipe elements within a permissible tolerance or the tolerances determining manufacturing acceptance must be tighter.
Thus, there is clearly a need for a pipe coupling which can be used with pipe elements having a generous tolerance range on parameters such as out of roundness and flare, yet will allow pipe elements to be inserted reliably without disassembly of the coupling.